Recently in an image data processing apparatus it is developed to edit for correcting or modifying images of photographs or pictorial arts by inputting them into personal computers as image data by using an image scanner.
However, it becomes need to compress the image data because of increasing of the capacity of a memory device which is necessary for storing the image data and also for an object of implementing a data communication or a data exchange to other apparatus, in accompanied with the increase of image data to be edited.
Now, as a high efficiency compression system of a still picture a block encoding system such as the JPEG (Joint Photographic Expert Group) system is commonly used.
If these image data compressing systems are supported in a hardware or a software of the image data editing apparatus, the compression of image data for storing may be carried out after the image editing. While if these image data compressing systems are not supported in such a hardware or a software, the compression of the image data may be carried out after storing them with an appropriate image format.
FIG. 1 is a block diagram showing one embodiment of the conventional image data compressing apparatus. A user performs an editing work on an image data by using a user interface 11. The image date is processed by a data processing means 12 in response to the input operation of the user. The processed image data is displayed on a monitor of an image display means 13. When storing the processed image data it is stored in a data storing means 15 such as a magnetic disc after compressing by a data compressing means 14.
In the image editing operation a paste work for pasting different small image on a base image is frequently carried out. For example it is frequently carried out to paste the image which had been cut out from any other secondary image and stored in a memory, on a primary image to be used as a base image.
Here when storing the edited image data by compressing based on the JPEG system, a compression rate or a picture quality extensively varies even though a image paste-in position has been slightly shifted. It is because a result of a quantization or an adaptive DCT processing varies in accordance with where a contour of the image is located within a 8.times.8 pixel block associated with a DCT (an abbreviation of Discrete Cosine Transform) operation.
However in a conventional image editing scheme as the editing of image data and a compression for storing images are completely independent to each other, it is not taken into account for an effect which a slight shift of the image paste-in position largely influences on the compression rate or the picture quality.
As described above, the conventional image data processing apparatus has such problems that as the editing of image data and a compression fop storing images are completely independent to each other, it is not taken into account for an effect which a slight shift of the image paste-in position largely influences on the compression rate or the picture quality thus causing the image data after compression to be left in large amount of volume.